Surgical gowns and drapes protect surgically prepared areas of the skin from contamination and also protect surgeons and nurses against contamination through contact with unprepared or contaminated areas of patient's skin. Preferably, surgical gowns should also present a sterile barrier to protect patients from contamination through contact with the surgeon, and vice versa.
Body liquids and other liquids can permeate through ordinary liquid resistant surgical gowns or drapes. Thus, bacteria, viruses, and bloodborne pathogens which may be present on one surface of the gown or drape may be transported through the gown to the patient or the operating room personnel. Thus, liquid imperviousness of the gown or drape is recognized as an important property.
It has been widely recognized that the gowns and drapes should be "breathable" to be comfortable, i.e., allow water vapor to pass through. It is not necessary that air pass through, only that water vapor from perspiration be transmitted from inside to outside so that undergarments do not become wet and so that a natural evaporative cooling effect can be achieved. Breathability and ability to transport interior moisture vapor to the external environment are used interchangeably herein, If a continuous film of hydrophilic material is exposed to air containing substantial water vapor on one side of the film, and to air containing less water vapor on the other side, the side of the film exposed to the higher water vapor concentration will absorb water molecules which diffuse through the film and are desorbed or evaporated on the side exposed to the lower water vapor concentration. Thus, water vapor is effectively transported through the film on a molecule by molecule basis. This property is known as "breathability".
Liquid water impermeability can be achieved in materials for use in surgical drapes and gowns by use of various impervious films such as polyethylene or plasticized PVC laminated to a fabric. Such fabrics are, however, not breathable and can be very uncomfortable to wear.
Both breathability and liquid water impermeability can be achieved readily with composite coatings of expanded porous polytetrafluoroethylene and hydrophilic polyurethanes. These coatings can then be attached to one or more layers of cloth to provide laminates which have all of the aforementioned properties desireable in surgical drapes and gowns.
However, the current trend of sterilizing operating room (O.R.) equipment, including surgical drapes and gowns, with ionizing radiation has thwarted efforts to use these polyurethane/expanded porous polytetrafluoroethylene composites because of degradation of the composite caused by the radiation. The radiation causes the composite to become gummy and to discolor.
This degradation of the composite is unexpected because generally polyurethanes are known to be resistant to degradation from ionizing or gamma radiation, as seen by Lawandy and Hepburn, Elastomerics 21-24, January 1981; and Klimanova, et al., Soviet Plastics No. 3, 23-25 (1973). Polymers in the former article, although showing signs of change, were still intact after 20 M. rads of cobalt 60 source gamma irradiation. In the latter article, exposures up to 200 M.rads are described and in several cases, the tensile strength was still higher after 200 M.rads dosage over the tensile strength unexposed samples. Polyurethane acrylates (Tu, SME Assoc. for Finish Processes, Sept. 1980 Conference, P. 117-143) sometimes develop color with either U.V. light or electron beam energy, and it has been reported that hindered phenols are effective in retarding color development.
In contrast to the stability of polyurethanes on exposure to ionizing radiation, expanded porous polytetrafluoroethylene is extremely sensitive to ionizing radiation, losing tensile strength even at less than one M.rad exposure in air. Thus, the composite, being made of a radiation stable polyurethane and a radiation unstable polytetrafluoroethylene would be expected to be better in stability than the polytetrafluoroethylene alone. However, the composite of polyuiethane and expanded porous polytetrafluoroethylene shows sensitivity to ionizing radiation similar to the sensitivity of the expanded porous polytetrafluoroethylene alone. That was unexpected because other properties of such coating composites resemble these of the polyurethane more than those of the expanded porous polytetrafluoroethylene.
It is mitigation of this sensitivity of such expanded porous polytetrafluoroethylene-polyurethane composites to ionizing radiation that this invention is directed.